In recent years, the Internet and the Internet-based services have developed rapidly, which brings great business opportunities for Internet Service Providers (ISPs) and imposes higher requirements on the backbone network. The MPLS technology is put forward to solve a series of problems arising in more and more large networks.
As a key technology of new network, MPLS is a tunneling technology, and is a routing and switching technology that integrates label switching and forwarding with network-layer routing, and ensures security of information transmission to some extent. On the MPLS network, if packets are forwarded by using label switching, the network routes can be controlled flexibly. The label switching is widely applicable to traffic engineering, Virtual Private Network (VPN), and Quality of Service (QoS). The path for forwarding packets in the MPLS network is a Label Switching Path (LSP).
In an MPLS architecture, a control plane is connectionless and based on the existing Internet Protocol (IP) network; the forwarding plane (namely, the data plane) is connection-oriented and based on layer-2 networks such as frame relay or Asynchronous Transfer Mode (ATM) networks. On the data plane, MPLS encapsulates packets with labels which are short and have a fixed length, and forwarded quickly. On the control plane, powerful and flexible routing functions are provided like in an IP network, thus fulfilling various network requirements raised by new applications.
The MPLS technology has some features different from the Interior Gateway Protocol (IGP), and the features are required for Traffic Engineering (TE). For example, the explicit LSP routing is supported, and the LSP is easier to manage and maintain in contrast with the traditional IP packet forwarding; the Label Distribution Protocol (LDP) which is constraint-based routing can implement various policies of TE; and the overhead of device in MPLS-based TE is lower than the overhead in other implementing modes. Therefore, the MPLS technology is applied to TE massively. On the IP network, the MPLS TE technology is a main technology for managing network traffic, reducing congestion, and ensuring Quality of Service (QoS) of the IP network. Through the MPLS TE technology, an LSP tunnel of a specified path is set up to reserve resources so that the network traffic bypasses the congested node and is balanced. In the case that the resources are stringent, the bandwidth resources of LSP tunnel with a low priority is occupied to meet the requirements of high-bandwidth LSP tunnels or important services; and when the LSP tunnel is faulty or a network node is congested, protection is provided by using Fast ReRoute (FRR) and path backup.
Through the MPLS TE technology, the network administrator can eliminate network congestion by only setting up some LSP tunnels and bypassing the congested nodes. With the increase of the LSP tunnels, a special offline tool may be used to analyze the traffic. For more details about MPLS TE, see Request For Comments (RFC) 2702 “Requirements for Traffic Engineering Over MPLS”.
In MPLS TE, the LSP which is set up based on certain constraint conditions is called a Constraint-based Routing LSP (CR-LSP). Unlike the setup of an ordinary LSP, the setup of a CR-LSP not only depends on routing information, but also needs to meet other conditions such as the specified bandwidth, selected path, or QoS parameters. During the network operation, traffic switching happens when the tunnel configuration is modified by the user, FRR switches, or the active LSP is faulty. Therefore, a standby LSP corresponding to the current active LSP needs to be set up under the same tunnel. The traffic is switched to the standby LSP when the ingress node perceives unavailability of the active LSP, and switched back upon recovery of the active LSP. In this way, the active LSP is protected with a standby mechanism.
Two standby modes are provided in the prior art: Hot-Standby (HSB) and ordinary standby.
The establishment of a standby CR-LSP accompanies the establishment of the active CR-LSP. When the active CR-LSP is faulty, the traffic is switched to the standby CR-LSP directly through MPLS TE, which is known as HSB.
After the active CR-LSP is faulty, a standby CR-LSP is established, which is known as ordinary standby.
The standby CR-LSP offers an end-to-end path protection for the whole LSP.
For the MPLS-TE HSB, the traffic is switched to the standby path and switched back to the active path through signaling convergence. When the fault of the active LSP is detected by using the signaling of the control plane, the traffic is switched to the standby LSP; after the recovery of the active LSP is detected by using the signaling, the traffic is switched from the standby LSP back to the active LSP.
However, the requirement for fast switching is not fulfilled in the foregoing process; that is, the fault of the active LSP is detected by using the signaling convergence of the control plane, and the switching result information is delivered to the forwarding plane, and then the forwarding plane performs traffic switching.
To improve the switching speed, a fast switching method is put forward in the prior art. In this method, the active LSP of TE is correlated with the Bidirectional Forwarding Detection (BFD) of the forwarding plane, and the fault of the active LSP is detected quickly by using the BFD, thus achieving fast switching.
FIG. 1 is a schematic diagram of a fast switching system in the prior art. As shown in FIG. 1, the system includes a Provider Edge router 1 (PE1), a PE2, a provider router (P1) and a P2. In HSB mode, a TE tunnel from the PE1 to the PE2 is set up. The active LSP passes through the P2; the standby LSP passes through the P1; and the active LSP is correlated with the BFD. On the control planes of PE1 and PE2, MPLS forwarding entries are created, including: Incoming Label Map (ILM), Next Hop Label Forwarding Entry (NHLFE), and Forwarding Equivalence Class-to-NHLFE Map (FTN). Such MPLS forwarding entries are delivered to the forwarding plane. On the control planes of P1 and P2, the MPLS forwarding entries “ILM” and “NHLFE” are created, and delivered to the forwarding planes of P1 and P2. The traffic runs over the active LSP through the P2 to the PE2, and is forwarded by the PE2.
When the PE1 perceives fault of the active LSP by using the BFD correlated with the active LSP, the traffic is switched to the standby LSP quickly on the forwarding plane. The traffic runs over the standby LSP through the P1 to the PE2, and is forwarded by the PE2.
When the PE1 perceives that the fault of the active LSP is rectified by using the signaling and the traffic needs to be switched back, the active LSP is set up again by using the signaling protocol of the control plane. An ILM and an NHLFE are delivered from the control plane to the forwarding plane, and the traffic is switched back to the active LSP. Currently, two modes for switching back are available: a mode for instantly switching back, and the other mode for switching back with delay.
In the mode for instantly switching back, the active LSP is set up again by using the signaling protocol of the control plane, and then is perceived by the PE1 by using the signaling. The ILM and NHLFE forwarding entries are delivered from the control plane to the forwarding plane in PE1 and an indication of directing the FTN to the active LSP NHLFE or an indication of setting the state of the active LSP to “up” is carried in the entries. The traffic is switched back to the active LSP in forwarding plane and sent to the P2. While the ILM and NHLFE forwarding entries are delivered to the forwarding plane in PE1, the ILM and NHLFE forwarding entries are delivered from the control plane to the forwarding plane in P2.
In the mode for switching back with delay, the active LSP is set up again by using the signaling protocol of the control plane, and then is perceived by the PE1 by using the signaling. The ILM and the NHLFE are delivered from the control plane to the forwarding plane in PE1. When the time setting for delay is out, the PE1 directs the FTN to the active LSP NHLFE, or sets the state of the active LSP to “up” through an indication. At this time, the traffic is switched back to the active LSP, and sent to the P2.
However, in the foregoing process, for the mode for instantly switching back, it is possible that the delivery of the ILM forwarding entries is not synchronous with the delivery of the NHLFE forwarding entries, which leads to traffic loss. For example, the delivery of the forwarding entries in PE1 is not synchronous with the delivery of the forwarding entries in P2, or the speed of the delivery is different. That is, if the forwarding entries are delivered more quickly in the PE1 than that in the P2, the traffic on the PE1 is switched back to the active LSP first. When the traffic of the PE1 arrives at the P2, the delivery of the forwarding entries is not complete in the P2 (for example, numerous route convergence is processed in the P2). In this case, the traffic loss occurs, which affects the availability and stability of the network drastically.
For the mode for switching back with delay, the traffic loss may be avoided through adjustment of the time for delay. However, it is hard to determine the time for delay. When the traffic is switched back, if the time for delay is set long, the switching back delay is also long, which affects the user experience and leads to a waste of network resources; if the time for delay is set short, the forwarding entries may not set up in the forwarding plane of P2 yet, which leads to traffic loss at the time of switching back, and affects the user experience and the network availability and stability.